Cooling and lubricating system for absorption refrigeration apparatus



Augn'ZB, 1966 w. OSBORN 3,257,691

COOLING AND LUBRICATING SYSTEM FOR ABSORPTION REFRIGERATION APPARATUS 2Sheets-Sheet 2 Filed Oct. 25, 1964 United States Patent 3,267,691COOLING AND LUBRKCATING SYSTEM FOR ABSORPTION REFRIGERATION APPARATUSWilliam L. Osborn, York, Pa., assignor to Borg-Warner Corporation, acorporation of Illinois Filed Oct. 23, 1964, Ser. No. 406,011 5 Claims.(Cl. 62-476) This invention relates generally to systems for providingcooling and lubricating fluid to the hermetically sealed, combinationpump-motor units in an absorption refrigeration apparatus, and moreparticularly to a cooling and lubricating system which automaticallymaintains an adequate supply of dilute absorbent solution of the properconcentration for use as a cooling and lubricating medium.

It will be appreciated that there are several different conventionalarrangements used in absorption refrigeration systems. For purposes ofillustration only, the description herein will relate to a designcomprising a pair of shells arranged one on top of the other, it beingunderstood that the invention is applicable to single shell and variousother configurations. In the example, the lower shell houses two tubebundles, the evaporator and the absorber, operating at a pressure on theorder of 6.3 mm. of Hg absolute ,5 atmosphere) while two tube bundles inthe upper shell provide a generator and a conenser, said shell beingmaintained at a pressure on the order of 75 mm. of Hg absoluteatmosphere).

As is Well-known to those skilled in the art, operation of the systemdepends on two factors: a refrigerant that boils at a temperature belowthat of the liquid being chilled and an absorbent possessing greataffinity for the refrigerant. At the pressures maintained within the twoshells, the water flowing over the bundle from the evaporator boils andextracts heat from the chilled liquid flowing through the tube bundle.Several refrigerant-absorbent combinations are used commercially, butthis specification will make reference to a system employing water asthe refrigerant and a hydroscopic brine such as LiBr as the absorbent,it being understood that the invention is applicable to otherrefrigerant-absorbent combinations.

A liquid, usually water, to cool the conditioned space or process ischilled as it passes through the evaporator tubes by giving up hea t tothe refrigerant flowing on the outside of the tubes. The heat removedfrom the chilled liquid causes the refrigerant (water) to evaporatesince it is at a pressure (with a corresponding boiling temperature)lower than the leaving chilled water temperature. For example, water ischilled from 54 F. to 44 F. with the evaporator at 6.3 mm. of Hgabsolute; this corresponds to a 40 F. boiling point for the refrigerant.

The LiBr solution, which is circulated within the absorber sectionlocated underneath the evaporator, has a great affinity for the watervapor released in the evaporator. This vapor flows downwardly and isbrought into contact with the intermediate strength solution flowingover the outside of the absorber tubes, thus diluting the solution. Theheat of absorption generated in this process is removed by condenserwater from a cooling tower or other source flowing through the absorbertubes.

Dilute solution from the absorber is pumped to the generator by thegenerator pump. In passing through the heat exchanger, it isregeneratively heated by hot, concentrated solution flowing from thegenerator to the absorber.

The dilute solution from the absorber flows over the outside of thegenerator tubes, and a portion of the refrigerant in the solution isvaporized by a heat exchange medium, usually steam, passing through thegenerator tubes. When the refrigerant is driven ofl, the solution isconcentrated and the concentrated solution fiows by gravity through theheat exchanger (where it is cooled regeneratively by the cold dilutesolution) to the suction side of the absorber pump.

The refrigerant vapor released from the boiling action in the generatorflows upwardly and is brought into contact with the outside of thecondenser tubes. The vapor gives up its heat of condensation to thecondenser water passing through the tubes and the condensed vapor ispassed through a conduit to a distributor located above the absorbercoil in the lower shell.

The absorption design described above is described more fully incopending application SN 169,969, filed January 30, 1962 now abandoned.The present invention relates more specifically to a system for coolingand lubricating the hermetically sealed pump and motor units whichcirculate solution and refrigerant through the system. It should beunderstood that this background description is merely for the purpose ofsetting forth the essential elements in a typical absorptionrefrigeration machine, and provides a basis for a clear understanding ofthe operation of the cooling and lubricating system associatedtherewith.

It has been found that dilute LiBr provides an excellent cooling and asuperior lubricating medium, requiring less maintenance than systemswhich utilize the re frigerant, i.e. water, for this purpose. However,one problem has been with insuring that an adequate supply of solutionhaving the proper concentration is available to compensate for leakagefrom the cooling and lubricating circuit into the solution circuit, orvice-versa. For one thing, the system must provide means for maintainingthe solution used for cooling and lubricating in a relatively dilutecondition; otherwise, when the solution is passed through the heatexchanger, where its temperature is lowered by a secondary coolant,there would be a possibility of LiBr salt crystallizing out of thesolution and choking off flow through the cooling circuit. On the otherhand, the concentration should be high enough to provide superiorlubricating properties. A range which has been found to be satisfactoryis between -53% LiBr.

It is therefore a principal object of the present invention to providean improved system for cooling and lubricating the hermetically sealedpump and motor units in an absorption refrigeration system.

Additional objects and advantages will be apparent from the followingdetailed description taken in conjunction with the drawings wherein:

FIGURE 1 is a schematic representation of a cooling and lubricatingsystem constructed in accordance with the principles of the invention;

FIGURE 2 is a view, partly in cross-section, of solution chamber;

FIGURE 3 is a cross-sectional view taken along the plane of line 33 ofFIGURE 2; and

FIGURE 4 is a cross-sectional view taken along plane of line 44 ofFIGURE 2.

Referring now to the drawings, and particularly to FIGURE 1, thereference character A designates a heat the the

exchanger in which the dilute absorber solution used for cooling andlubricating the pump-motor units passes in heat exchange relation with asecondary cooling fluid. In a preferred embodiment, this secondarycooling fluid is provided by tapping off cold refrigerant from therefrigerant line.

Reference character B designates a concentration control and make-upsolution chamber. This chamber, hereinafter referred to as the solutionchamber, has several functions. First of all, it acts as a make-upchamber for solution which provides additional solution to the coolantcircuit in the event the leakage is from the latter into therefrigerant/solution circuit. It also permits any excess solution, dueto leakage from the refrigerant/solution circuit, to flow back to theabsorber. Another important function is to maintain the coolant solutionat the proper concentration; if it is too dilute, water is drawn out ofthe solution; if it is too concentrated, water is added. How this isaccomplished will be clear from a later description of. the operation.

While all of the pump-motor units ordinarily provided in an absorptionrefrigeration system are not shown, it will be appreciated that mostsystems include a generator pump for pumping dilute absorbent solutionfrom the absorber to the generator, a refrigerant pump for recirculatingrefrigerant through the evaporator and an absorber pump forrecirculating an intermediate strength solution through the absorber. Ineach case, solution is passed into and throughthe casing of each unit ina manner similar to that described in copending application SN 317,661,filed October 21, 1963. It will be understood that each of thepump-motor units has a motor section and a pump section, thecooling-lubricating solution passing into and out of the motor sectiononly. Each of the motor shafts, as illustrated in the aforementionedcopending application, also carries a small impeller which pumps thesolution through the casing and back to the heat exchanger.

As shown in FIGURE 1, the generator pump 10 is provided with dischargeline 11 through which dilute solution from the absorber is forwarded tothe generator (not shown). A tap-off conduit 12 communicates with thedischarge line and carries a portion of this solution to the solutionchamber B.

Solution chamber B comprises a cylindrical shell 16 having end closures17, 18, a divider plate 2i? extending transversely across the chamberand being provided with aperture 21, a weir 22, and a perforateddistributor plate 24. Located in the zone to the right of weir 22 (FIG-URES 1 and 2) is a solution over-flow line 26 leading back to theabsorber. Communicating with the zone to the left of divider plate is aconduit 27 which interconnects with the shell side of heat exchanger A.In this same zone is a conduit 28, which may be referred to as anequalizing line, having a terminal portion extending upwardly into theupper part of the solution chamber and the opposite end terminating inthe upper portion of the absorber. The function of this equalizing linewill be apparent from the description of the operation.

The circuit for the primary coolant, i.e. the coolant which comesdirectly in contact with the pump-motor units, includes the conduit 27connecting the solution chamber B with heat exchanger A, conduit 38leading from the lower portion of the shell side of said heat exchanger,a filter or strainer element 32, and a supply header 34. Individualsupply lines for the coolant solution include lines leading to therefrigerant pump 40, line 36 leading to the absorber pump whichcirculates an intermediate strength solution over the absorber tubebundle (not shown), and line 37 leading to the pumpmotor unit for thegenerator. As mentioned above, each of the pump-motor units includes anauxiliary pumping device for circulating the coolant solution in thecasing in heat exchange relation with the motor armature and bearings.Coolant solution is returned through lines 41, .2,

and 43 to a return header 44 which delivers the solution to an inlet 45in the upper portion of the heat exchanger A. A portion of the solutionfrom return header flows upwardly through conduit 46 to an opening inthe solution chamber B above the distributor plate 24'.

Heat exchanger A may take the form of a conventional tube and shell heatexchanger design comprising a generally cylindrical shell 5t? and acoiled tube 55 arranged therein. The conduit 27 which interconnects theshell side of heat exchanger A with solution chamber B opens into theshell at the upper portion thereof while conduit 3t which carries thecooled solution to the pump-motor units, is connected to the lowerportion of said shell. The inlet line 45 which is employed to returnsolution to the heat exchanger after passing through the pump-motorunits is connected at the opposite end of the heat exchanger shell nearthe upper portion thereof, said inlet line as, in a preferredembodiment, being provided with an orifice 49 to insure that a portionof the returning fluid is directed upwardly to the solution chamber Bthrough conduit 46.

Operation From the individual pump-motor units, the coolant solutionflows through lines 41, 42, and 43 into the header as. The flow ofreturning coolant is split into two streams, one of which flows throughinlet line 45 to the heat exchanger A and the other flowing through line46 to the solution chamber B where it is discharged downwardly againstthe perforated. distributor plate 24. The solution impinges against thedistributor plate where it is broken into small droplets which fall inrain-like fashion on the surface of the solution. The solution thenflows by gravity through line 27 into the heat exchanger where itcombines with the solution being returned from the pumpmotor unitsthrough line 45. The latter flows from right to left (as shown inFIGURE 1) and is cooled by passing over tube 55 through which coldrefrigerant (approximately 40 F.) circulates. The refrigerant, it willbe noted, is tapped olf from line 56 by a line 57 connected to coiledtube 55 and is returned to the inlet side of refrigerant pump 40 vialine 58. Solution in .heat exchanger A passes downwardly through conduit30, filter 32, and supply header 34 to the individual branch supplylines lead-' ing to the pump-motor unit through lines 35, 36, and 37.

Should leakage be encountered in the pump-motor shaft seal, therebycausing fluid in the pump section of one of the pump-motor units, eitherwater or LiBr, to enter the motor coolant-lubricant circuit, the excessfluid will flow through the aperture 21 to the right-hand portion of thesolution chamber. This solution will overflow weir 22 and be passedthrough the over-flow line 26 to the absorber. On the other hand, shouldthe leakage be from the motor coolant-lubricant circuit into thesolution/refrigerant circuit, additional make-up solution will beprovided from the generator solution entering via conduit 12 chamber 16through divider plate 20. Solution flow in this case would be from theright-hand half of the chamber through opening 21 to the left-hand halfof the chamber.

The system further provides automatic control over the concentration ofthe motor coolant-lubricant solution. If the concentration of thesolution begins to rise, its vapor pressure will be depressed, assumingthat the temperature will remain relativelyconstant. This will causewater vapor from the absorber to pass through line 28 and be absorbed bysolution in the zone in the upper portion of the solution chamber. Thissame mass transfer opera tion will work in reverse if the solutionconcentration drops. In this case, the vapor pressure of the solutionwill rise, causing water vapor to flow to the lower pressure area in theabsorber through line 28. This will restore the chamber equilibrium and,thus, return the solution to its normal operating concentration range.

For example, in a LiBr system which is operating at a 40 refrigeranttemperature in the evaporator, the vapor pressure in the absorber wouldbe approximately 6 mm. Hg absolute. Recirculated solution entering thesolution chamber B from line 46 is cooled to some temperature in theneighborhood of 75 F., and the equilibrium condition at 6 mm. pressureand 75 F. corresponds to a concentration of 50% LiBr solution by weight.Operating at this condition, the solution will come up to equilibrium atthis 50% value. If, however, on start-up, the solution concentrationtended to be somewhat greater than this, for example 55% by weight ofLiBr, then the corresponding vapor pressure at 75 F. would beapproximately 3.2 mm. Hg absolute. Consequently, the solution would tendto absorb water vapor from the absorber through line 29 untilequilibrium is established. At 6 mm. of pressure and 75 F. as notedabove, this would result in a final equilibrium of 50% solution. Inorder to insure that this equilibrium condition is established quickly,the perforated plate 24 is used to break up the solution into smalldroplets which fall through the vapor chamber and thus affordconsiderable absorber surface.

If solution enters chamber B through line 46 at a lower temperature, say65 F., then solution would come to a new equilibrium point ofapproximately 45%. Similarly, if the solution temperature would be at 85F., the equilibrium point would be approximately 53% LiBr. In any event,the resulting concentration of solution in the lubricant and coolantcircuit is kept within a range of about 45 to 53%, appreciably lowerthan the main solution circuit concentration. Within this range, thesolution is sufliciently high in concentration to provide the desirablelubrication surface and at the same time is safely below theconcentration where crystallization might result.

While this invention has been described in connection with a certainspecific embodiment thereof, it is to be understood that this is by wayof illustration and not by way of limitation; and the scope of thisinvention is defined solely by the appended claims which should beconstrued as broadly as the prior art will permit.

What is claimed is:

1. In an absorption refrigeration system including a generator, acondenser, an evaporator, and an absorber connected in a closedrefrigeration circuit, and a plurality of hermetically sealed pump-motorunits for circulating solution and refrigerant through said system, acooling and lubricating circuit comprising a heat exchanger; means forcirculating a liquid coolant in a first path through said heat exchangerand said pump-motor units; a solution chamber connected to provide asecond path for coolant in parallel with said heat exchanger; means forcontinuously supplying absorbent solution from said refrigerationcircuit to said solution chamber; conduit means for interconnecting saidabsorber and said solution chamber to provide a passage for water vaporflow to and from said absorber in order to establish a concentration ofsaid coolant solution somewhat below the normal concentration ofsolution flowing within the refrigeration circuit; and means forsupplying a secondary coolant to said heat exchanger such that it passesin indirect heat exchange relation to the solution flowing therethrough.

2. In an absorption refrigeration system including a generator, acondenser, an evaporator, and an absorber connected in a closedrefrigeration circuit, and a plurality of hermetically sealed pump-motorunits for circulating solution and refrigerant through said system, acooling and lubricating circuit comprising a heat exchanger; means forcirculating a liquid coolant through a first path including said heatexchanger and said pump-motor units; a solution chamber connected inparallel with said heat exchanger; means for circulating liquid coolantin a second path including said heat exchanger and said solutionchamber; means for continuously supplying absorbent solution from saidrefrigeration circuit to said solution chamber in such a manner thatadditional solution is added to the flow of coolant in said second pathas required; means for interconnecting said absorber and said solutionchamber to provide a passage for water vapor flow to and from saidabsorber in order to establish a concentration of said coolant solutionsomewhat below the normal concentration of solution flowing within therefrigeration circuit; and means for supplying a secondary coolant tosaid heat exchanger such that it passes in indirect heat exchangerelation to the coolant flowing to said pump-motor units.

3. In an absorption refrigeration system including a generator, acondenser, an evaporator, and an absorber connected in a closedrefrigeration circuit, and a plurality of hermetically sealed pump-motorunits for circulating solution and refrigerant through said system, acooling and lubricating circuit comprising a heat exchanger; means forcirculating a liquid coolant, consisting essentially of an aqueoussolution of LiBr having a concentration on the order of 50% by weightLiBr, from said heat exchanger to said pump-motor units and back; asolution chamber connected in parallel with and above said heatexchanger, means in said solution chamber for maintaining the solutiontherein at a fixed level, said means including an overflow line whichpermits excess solution to flow back to said absorber and means forcontinuously supplying absorbent solution from said refrigerationcircuit to said solution chamber; means for interconnecting saidabsorber and said solution chamber to provide a passage for water vaporflow to and from said absorber in order to establish a concentration ofsaid coolant solution somewhat below the normal concentration ofsolution flowing within the refrigeration circuit, and means forsupplying a secondary coolant to said heat exchanger such that it passesin indirect heat exchange relation to the solution flowing therethrough.

4. In an absorption refrigeration system including a generator, acondenser, an evaporator, and an absorber connected in a closedrefrigeration circuit, and a plurality of hermetically sealed pump-motorunits for circulating solution and refrigerant through said system, acooling and lubricating circuit comprising a shell and tube heatexchanger having a shell side and a tube side; a solution chamberlocated above said heat exchanger; means for continuously supplyingsolution from said refrigeration circuit to said solution chamber; firstconduit means interconnecting said solution chamber with said heatexchanger such that solution flows by gravity from the solution chamberthrough the shell side of said heat exchanger; a weir in said solutionchamber, said weir determining the level of liquid within said solutionchamber; an overflow conduit for carrying solution overflowing said weirto said absorber; second conduit means for conducting coolant solutionfrom the shell side of said heat exchanger through said pump-motor unitsin heat exchange relationship therewith, third conduit means forcirculating a portion of the coolant being returned to said heatexchanger back to said solution chamber, said solution being introducedin such a manner that said solution is broken up into small droplets toprovide a relatively large absorber surface area; fourth conduit meansinterconnecting said absorber and said solution chamber to provide apassage for water vapor flow to and from said absorber whereby theequilibrium concentration of the coolant solution introduced into thechamber by said third conduit means is quickly established; and meansfor supplying a secondary coolant through the tube side of said heatexchanger.

5. Apparatus as defined in claim 1 wherein said solution chambercomprises an elongated cylindrical shell; partition means dividing saidshell into a first zone and a second zone; aperture means through saidpartition means to provide fluid communication between said zones; aweir disposed within said first zone, the upper edge of said weir beinglocated above said aperture means; first conduit means interconnectingthe lower part of said second zone to said heat exchanger.

References Cited by the Examiner UNITED STATES PATENTS Leonard 62494Edberg et a1 62-505 X Rayner 62-505 Enibury et a1. 62505 X LLOYD L.KING, Primary Examiner.

1. IN AN ABSORPTION REFRIGERATION SYSTEM INCLUDING A GENERATOR, ACONDENSER, AN EVAPORATOR, AND AN ABSORBER CONNECTED IN A CLOSEDREFRIGERATION CIRCUIT, AND A PLURALITY OF HERMETICALLY SEALED PUMP-MOTORUNITS FOR CIRCULATING SOLUTION AND REFRIGERANT THROUGH SAID SYSTEM, ACOOLING AND LUBRICATING CIRCUIT COMPRISING A HEAT EXCHANGER; MEANS FORCIRCULATING A LIQUID COOLANT IN A FIRST PATH THROUGH SAID HEAT EXCHANGERAND SAID PUMP-MOTOR UNITS; A SOLUTION CHAMBER CONNECTED TO PROVIDE ASECOND PATH FOR COOLANT IN PARALLEL WITH SAID HEAT EXCHANGER; MEANS FORCONTINUOUSLY SUPPLYING ABSORBENT SOLUTION FROM SAID REFRIGERATIONCIRCUIT TO SAID SOLUTION CHAMBER; CONDUIT MEANS FOR INTERCONNECTING SAIDABSORBER AND SAID SOLUTION CHAMBER TO PROVIDE A PASSAGE FOR WATER VAPORFLOW TO AND FROM SAID ABSORBER IN ORDER TO ESTABLISH A CONCENTRATION OFSAID COOLANT SOLUTION SOMEWHAT BELOW THE NORMAL CONCENTRATION OFSOLUTION FLOWING WITHIN THE REFRIGERATION CIRCUIT; AND MEANS FORSUPPLING A SECONDARY COOLANT TO SAID HEAT EXCHANGER SUCH THAT IS PASSESIN INDIRECT HEAT EXCHANGE RELATION TO THE SOLUTION FLOWING THERETHROUGH.